this is brads quote from the page that makes me think that.

The results decided which header/muffler combination went on this 888 for sale, and which one stayed for the 851. That means the 851 is keeping its std ST4 headers and the Staintunes. I was hoping the std ST4 headers would out-do the DP headers a little, but certainly wasn’t looking forward to that hole in the curve. Makes the all std to final "as to be sold" result graph look a bit lame in comparison to what it could be.

where did you get all that technical waffle from anyway?
the rest of the article explains how the larger diameter allows better breathing at high revs, so it depends on the flavour of your compromise.

All a bit much eh, that stuff in the link. 4th last paragraph in the link gives the 50mm truth. He sells the lemon, and keeps the std ST4. "The DP system turned out to be a bit of a non performer", is his quote.
Where do i get this technical waffle? I have already been part of a engine build team on a rather wicked 650 pantah race engine in 1984. Mr Personality and his old partner, the original Mr Personality are no fools. What Brad did with a dyno, they did with pencils and calculators. Even built the headers from scratch, using fomulas from a 1950's book! Beast of a bike!

Reading the moto - one stuff and Ian Falloons book it appears that the critical ratio is the valve vs header diameter. Since the later 888s and the SP2/3 have the same valve sizes and the SP2/3 exhaust has 50mm headers, this seems to be the way to go for a cost effective power increase.

Douglas

Yes that sounds fair, but the header has a taper and this gets thrown into it aswell. As well as the port size. The port size comes into it if you have just thrown in a set of bigger valves and not increased the port size. All that exaust gast escapes into the port at x pressure and velocity. Then it enters the header. If the diameter of the header is too large, the gas then expands into the header and drops velocity and increases pressure, and throws the whole thing out of whack.
The taper, from memory, should be finished 13 inches from the valve. this enables the correct forming of the shock wave. This shock wave is responsable for pushing the the remainder of the exhaust charge back down the port and partially into the chamber, thereby pre pressurising, getting ready for the incoming fuel/air charge. In regards to the std ST4 headers, are they the same ratios as the 888 and SP2/3 headers? My guess is that they are different. Hence the 45mm system works well. But As I don't have any to measure I am only guessing.

When I get around to it I'll be putting std ST4 headers on my 851 I think.With Staintune cans. They dont fall apart or rust.
Griff

so the D/P st4 headers are just too big and leave a BIG dip in the power curve, the std st4 system gives more everywhere but still has a pronounced dip in the curve. no surprise really as it wasn't designed for a 888 to begin with. if the SP style headers are unavailable they would be the next choice, but i'd prefer the SP ones to those.
i'm guessing Mr Personality is bob? who is the "original Mr Personality?
and pencils and calculators with a 1950's book may have done the job in the day, but you can't belittle brad at moto one' efforts nor his dedication to actually SUPPLY the information the fruits of his labour produce. none of this is black magic, it's just that some would have us believe so.:sing:
cheers,
paul.

Having been a frequent visitor to Moto-one, I would not belittle Brad, what he has done and published is bloody fantastic. It makes life so much easier and basically cuts to the chase, removing any shall we say worshop wondering.

As for the SP headers, I couldn't say having not seen the data on them. It maybe that the ST4 are better as they were designed a couple of years later. But you can bet that the Sp ones defiantely would an improvement on the standard.

The original Mr Personality is a bloke called Blair MacIntosh.

Griff

the SP ones are a definite improvement on std headers as far as allowing the motor to rev easier and provide more power up top, say from 7000 thru redline. the downside is they reduce bottom end dramatically, especially on a bike that is close to std. that's what happened with mine anyway.:burn: